1. Field of the Invention
The present invention relates to a method for improving a high speed downlink operation corresponding to a CELL_FACH state for a wireless communications system and related communications device, and more particularly to a method for improving a determining procedure of stopping a high speed downlink operation corresponding to a CELL_FACH state for a UE in the CELL_FACH state for a wireless communications system and related communications device.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting at the third generation mobile telecommunication technology, the 3rd Generation Partnership Project (3GPP) provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate.
On the basis of HSDPA, the 3GPP further introduces HS-DSCH reception in a CELL_FACH state allowing the UE in the CELL_FACH state to monitor a High Speed Downlink Shared Channel (HS-DSCH) accompanied with a Shared Control Channel for HS-DSCH (HS-SCCH) for downlink data reception, so as to improve a peak data rate, a signaling delay, a state transition delay, download times and flexible cell capacity.
A UMTS radio access network (UTRAN) enables the HS-DSCH reception in the CELL_FACH state by including parameters, related to radio resource control (RRC) configuration of HS-SCCH, HS-DSCH and a common HS-DSCH radio network transaction identifier (common H-RNTI), in the system information broadcast. For the UE in an idle mode, the parameters are configured in a “Downlink HS-PDSCH system information” information element (IE) included in a system information block (SIB) type 5/5bis. For the UE in an RRC connection mode, the parameters are configured in a “Downlink HS-PDSCH system information for connected mode” IE included in an SIB type 6.
The UE may use a common or a dedicated H-RNTI to perform the HS-DSCH reception in the CELL_FACH state. The common and dedicated H-RNTIs are both used as an identity of the UE so that the UE can receive its own packets. Furthermore, the common H-RNTI can be shared by multiple UEs, whereas each dedicated H-RNTI is only allocated to one UE. During reception of media access control (MAC) packets, the UE using the common H-RNTI needs to determine whether the received packets belong to it via UE identification information (i.e. UE ID and UE ID Type) in the packet header. On the other hand, the MAC packets for the UE using the dedicated H-RNTI include no UE identification information to provide better data transmission efficiency.
The UE selects a suitable common H-RNTI to use from the common H-RNTI parameter. On the other hand, if the UTRAN attempts to allocate a dedicated H-RNTI to the UE, the UTRAN sends a related configuration through RRC procedures, such as an RRC connection or a cell update procedure, and the UE stores the configuration in an H-RNTI variable. Each time the HS-DSCH reception in the CELL_FACH state is enabled, the UE uses the dedicated H-RNTI if the H-RNTI variable is set; otherwise the UE uses the common H-RNTI.
The UE has an HS_DSCH_RECEPTION_CELL_FACH_STATE and an HS_DSCH_RECEPTION_OF_CCCH variable revealing a use state of the dedicated and common H-RNTIs, respectively. When the HS_DSCH_RECEPTION_CELL_FACH_STATE variable is set to “TRUE”, the UE receives packets mapped to a Dedicated Traffic Channel (DTCH) and a Dedicated Control Channel (DCCH) according to the dedicated H-RNTI. When the HS_DSCH_RECEPTION_OF_CCCH variable is set to “TRUE”, the UE receives packets mapped to a Common Control Channel (CCCH) according to the common H-RNTI. If both of the variables are set to “FALSE”, this means that the HS-DSCH reception in the CELL_FACH state is deactivated.
According to the RRC specification, the UE has to perform a variable determining procedure to activate or deactivate the HS-DSCH reception in the CELL_FACH state. For applying the HS-DSCH reception in the CELL_FACH state, the following conditions must be met: (1) the UE is in the CELL_FACH state; (2) the variable H-RNTI is set; (3) the SIB type 6 is defined and includes the “Downlink HS-PDSCH system information for connected mode” IE or the SIB type 5/5bis includes the “Downlink HS-PDSCH system information for connected mode” IE. If all the conditions are met, the variable HS_DSCH_RECEPTION_CELL_FACH_STATE is set to “TRUE” for starting HS-DSCH reception in low layers (the MAC and physical layer).
If any of the above conditions is not met and the HS_DSCH_RECEPTION_CELL_FACH_STATE variable is set to “TRUE”, the UE sets the variable to “FALSE”. In addition, if the UE is in the CELL_FACH state and the HS_DSCH_RECEPTION_OF_CCCH variable is set to “FALSE”, the UE stops the HS-DSCH reception and sets an INVALID_CONFIGURATION variable to “TRUE”, which means that the settings of the HS_DSCH_RECEPTION_CELL_FACH_STATE and HS_DSCH_RECEPTION_OF_CCCH variables are considered an invalid RRC configuration. In this situation, the UE may disconnect the RRC connection and enter the idle mode.
As can be deduced from the above, the situation causing the UE in the CELL_FACH state to change the HS_DSCH_RECEPTION_CELL_FACH_STATE variable from “TRUE” to “FALSE” is either the variable H-RNTI is cleared or the SIBs type 5/5bis and type 6 do not indicate the support of HS-DSCH reception in the CELL_FACH state.
The UE may initiate the cell update procedure during the HS-DSCH reception in the CELL_FACH state, and the cause to initiate the cell update procedure may be cell reselection, periodical cell update, a radio link failure, an RLC unrecoverable error or uplink data transmission. The UE also initiates a URA update procedure when performing UTRAN registration area reselection (URA Reselection) or periodical URA update.
When the UE initiates the cell/URA update procedure due to cell/URA reselection and the selected cell/URA supports the HS-DSCH reception in the CELL_FACH state, the H-RNTI variable storing the dedicated H-RNTI is cleared, and the HS_DSCH_RECEPTION_OF_CCCH variable is set to “TRUE” for the UE to perform the HS-DSCH reception with the common H-RNTI.
If the selected cell/URA does not support the HS-DSCH reception in the CELL_FACH state, neither the SIB type 6 includes the “Downlink HS-PDSCH system information for connected mode” IE nor does the SIB type 5/5bis include the “Downlink HS-PDSCH system information for connected mode” IE. As a result, the HS_DSCH_RECEPTION_CELL_FACH_STATE variable changes from “TRUE” to “FALSE”. In this situation, the INVALID_CONFIGURATION variable is set to “TRUE” through the abovementioned variable determining procedure if the HS_DSCH_RECEPTION_OF_CCCH variable is set to “FALSE”. However, the settings of the HS_DSCH_RECEPTION_OF-CCCH and HS_DSCH_RECEPTION_CELL_FACH_STATE variables, which can be used for configuring the UE to perform a non-high speed downlink operation, should not be considered illegitimate in the above case. Furthermore, setting the INVALID_CONFIGURATION variable to “TRUE” configures the UE to disconnect the RRC connection, thereby resulting in repeated reconnections for packet reception. Thus, the variable determining procedure of the prior art degrades packet transmission performance.